1. Field of the Invention
This invention relates to an industrial adhesive tape comprising a tape-shaped textile dyed backing and a single- or both-sidedly applied adhesive, in particular pressure sensitive adhesive, coating.
2. Related Technology
Industrial adhesive tapes useful in the cable-wrapping sector in particular currently overwhelmingly utilize backing materials composed of viscose rayon staple wovens, polyester wovens or nonwovens.
Viscose rayon staple woven adhesive tapes have the disadvantage of being rottable and of a limited thermal stability up to about 100° C. The backing material is typically dyed, in particular black, with disperse dyes. Aging at elevated temperatures leads for these known tapes disadvantageously not only to a reduction in color quality but also in particular to a decomposition of the backing material, and can impair the compatibility of the tape with leads to be wrapped.
Polyester, in particular PET, woven adhesive tapes are unrottable and have a significantly higher breaking strength and a higher thermal stability than viscose rayon staple woven adhesive tapes. To obtain the black color desired in most cases for use as a cable-wrapping tape in the automotive industry, the wovens are dyed with disperse dyes. At temperature levels above 125° C., the disperse dye or its components are observed to migrate from the fabric, and this leads to a color change on the part of the fabric and in certain circumstances also on the part of the wrapped leads. The migrated entities may even, depending on the chemical identity of the insulating material used, impair the technical properties of the lead, such as breaking extension or thermal stability.
Nonwovens which, as will be known, are likewise used as a backing material for industrial adhesive tapes, in particular cable-wrapping tapes, likewise consist overwhelmingly of polyester. There are spunbonded nonwovens produced from continuous filaments and there are nonwovens produced from staple fibers of defined length. Nonwovens can be consolidated using different methods, such as stitching, needling, embossing or by means of a water jet. Nonwoven fabrics are likewise dyed with disperse dyes. At temperature levels above 125° C. the disperse dye is again observed to migrate out of the disperse-dyed materials, and this can potentially have the same adverse consequences for compatibility with the wrapped lead as described above for wovens.
Disperse dyeing, whether performed continuously (for example by thermosoling using an integrated pad-mangle) or batchwise (on a so-called beam or by using a “high pressure jigger”), white fabric is exposed to a dye in a bath. Dispersants are utilized as auxiliaries in order that uniform distribution of the dyes in the dispersion may be obtained. The dye in this dyeing process initially deposits around the fiber to then penetrate into it under the influence of heat and/or pressure. To prepare for the actual dyeing operation, the fabric can be desized or deoiled and/or pre-set in order that dye penetration may be facilitated. In the continuous thermosol process, the dyeing is subsequently heat-set.
Small dye molecules are utilized in rapid dyeing, while comparatively larger dye molecules are utilized in normal dyeing. Rapid dyeing, in addition to dye molecules, may employ dyeing accelerants known as carriers, such as benzenes, phenylphenols or dicarboxylic esters, which have an additional, fabric-plastizing effect. The above-described disadvantages of disperse-dyed backing materials, namely that they may decolorize at high temperatures and low molecular weight constituents may migrate out of the woven or nonwoven fabric, occur because of the high level of molecular mobility preferentially in the case of rapid dyeing, but also, depending on the temperature load, in the case of normal dyeing. Since carriers may also reduce color fastness, they are in many cases omitted and dyeing times lengthened.
About 20 to 25 percent of the dye used does not penetrate into the fabric and is present as excess dye, which then has to be removed again by a chemical aftertreatment, for example by reduction clearing with aqueous sodium hydroxide solution and hydrosulfite.
Especially cables to be used in automotive construction, including the adhesive tapes used for cable wrapping, have to meet a demanding performance profile. To verify that a material of construction meets existing performance requirements, various examinations and tests are prescribed. Examples to be mentioned here are the VW standard 60306, the test prescribed by Mercedes Benz AG for wrapping tapes for cableset production or the draft standards LV 112 (issued July 2003) or LV 312 (issued April 2004) agreed by various automotive manufacturers.
According to these standards, the material of construction used for insulating the leads shall meet the requirements of VDA 231-106. The minimum and maximum sustained use temperatures (TU and TO) for a use period of 3000 h are −40° C. and 100° C. (105° C. in the case of PVC insulation material) for a classification into temperature class B for example, and the material shall be capable of withstanding a short-temperature (240 hours) of 125±3° C. and an overload temperature (6 hours) of 150±3° C.
Aging performance is rated according to whether it is for a short term (240 h) or a long term (3000 h). Requirements and experimental conditions for both the tests are given by DIN ISO 6722-1 and -2. A wrapping test is performed at 25° C. after the short term aging and at room temperature after long term aging. A wrapping test is additionally carried out at low temperature (−40° C.), again according to DIN ISO 6722-1 and -2.
With regard to the compatibility of leads with other cableset components, such as the cable-wrapping tapes, here LV 112 provides, inter alia, for a test of media resistance against a Coroplast 837X adhesive tape of the aforementioned kind.
As very recent experience has shown, adhesive tapes can cause such pronounced discoloration of individual cables that the original color of an individual cable is no longer discernible. It is likely that the relevant testing methods will have to be supplemented with regard to discoloration, so that significant discoloration is no longer permissible in the future. When leads exhibit pronounced discoloration, there is a risk that in the event of service it is no longer possible to decide which lead in a cable harness performs which function.
The known backing materials described at the beginning are typically coated with an adhesive coating of hotmelt adhesives based on natural or synthetic rubber. Such adhesive tapes are used for sustained use at temperatures of not more than 100° C. (viscose rayon staple tapes) to 125° C. (polyester tapes), which corresponds to temperature classes A to C as defined by LV 112. Acrylate-based hotmelt adhesives have also come to be used of late. These adhesives possess better aging resistance than rubber adhesives and therefore, if combined with suitable backings, permit use of the tapes for the 150° C. temperature class (temperature class D). With regard to the compatibility or otherwise of the adhesives with the backing material and of the adhesive tapes with the electric leads, it has to be assumed that the adhesives used lead to interactions with the dyes used in the backing material or its components and to an influence on the migration of these components through the layer of adhesive into the core insulation of the leads.
Owing to their high degree of flexibility, their excellent noise-muffling properties and their favorable properties with regard to high abrasion resistance, it is desirable that adhesive tapes comprising textile backings also be used for high thermal load applications in lieu of film adhesive tapes or convoluted tubes. For these high thermal loads, however, the above-described dye migration constitutes a problem, in particular with regard to woven PET fabric.